The present invention relates to a developing device for use in an electrophotographic image forming apparatus, particularly a printer, facsimile apparatus or copier of the type using a toner and carrier mixture or bicomponent developer.
A developing device for the above application has developing means facing an image carrier on which a latent image is to be electrostatically formed. The developing means deposits a toner and carrier mixture on the image carrier to develop the latent image formed thereon. Various kinds of arrangements have heretofore been proposed in relation to the developing device, as follows:
(1) An arrangement wherein means for agitating a toner and carrier mixture or developer disposed in a photoconductive drum and communicated to a developing unit by a piping so as to circulate the developer (Japanese Patent Publication No. 5-21082);
(2) An arrangement for supplying a developer or carrier to the casing of a developing device, discharging the developer from the casing in the same amount as the developer or carrier fed, and replenishing toner in an amount matching toner consumed by development and determined by volume sensing means (Japanese Patent Publication No. 60-18065);
(3) An arrangement for detecting the density of a developer in terms of a change in volume (Japanese Patent Laid-Open Publication No. 50-19459);
(4) An arrangement consisting of developing section, means for supplying a preselected amount of carrier to the developing section on the elapse of a predetermined developing time or on the production of a predetermined number of copies, detecting means for detecting a change in the toner and carrier mixture ratio and generating a signal representing it, means for replenishing toner to the developing section in response to the signal, and means for discharging more than a predetermined amount of developer from the developing section (Japanese Patent Laid-Open Publication No. 51-13249);
(5) An arrangement for extending the life of a developer by replenishing the developer existing in a developing device with an additional toner and carrier mixture (Japanese Patent Laid-Open Publication No. 4-353881).
However, the conventional developing device with any of the above configurations has the following problems. A developing sleeve faces a photoconductive element or image carrier. The device has an accumulating portion in which the developer accumulates, and a hopper for replenishing fresh toner. The accumulating portion and hopper are located in the vicinity of the developing sleeve in order to supply the developer to the sleeve. Further, the accumulating portion and hopper are constructed integrally with the developing means which is implemented as a unit accommodating the sleeve. Such a configuration is bulky, complicates the construction of the entire developing device, and thereby obstructs maintenance.